Saitoh Sei

White matter abnormalities have been implicated in psychiatric diseases such as major depressive disorder (MDD) ; however, the underlying mechanisms remain poorly understood. The structure and function of the corpus callosum are particularly vulnerable to stress, which may lead to MDD. In the present study, we investigated whether chronic social defeat stress (CSDS) induces myelin abnormalities of the corpus callosum through inflammation that contributes to the pathogenesis of MDD. To produce CSDS, the adult C57BL/6J mouse was exposed to an aggressor ICR mouse for 10 consecutive days. CSDS decreased mature oligodendrocytes in the corpus callosum, and persistently developed depression-like behaviors such as increased immobility in the forced swimming test and impaired social interaction. On transmission electron microscopy, myelin abnormalities and axonal degeneration were observed with necrosis-like cell death of oligodendrocytes in the corpus callosum. Interestingly, CSDS significantly increased the Gasdermin D (Gsdmd), a marker of pyroptosis, concomitantly with enhanced IL-1β production in the corpus callosum. Administration of IL-1β inhibitor prevented the decrease of oligodendrocytes and CSDS-induced depression-like behaviors. These findings suggest that IL-1β acts as a crucial mediator of oligodendroglial pyroptosis induced by the CSDS, which may be responsible for the development of MDD.

The transport mechanism of soluble molecules throughout the interstitial matrix is closely associated with human tumor behavior in vivo. However, the examination of soluble components in histological architectures has been hampered by artifacts caused during conventional tissue preparation. In this study, the immunodistribution of intrinsic and extrinsic serum components in tumor tissues was examined in xenografted human tumor cells using 'in vivo cryotechnique' (IVCT) and cryobiopsy, where target tissues are directly cryofixed in vivo. Human lung cancer cells were subcutaneously injected into the dorsal flank of nude mice, and paraffin sections and cryosections of produced tumors were prepared with different methods. Immunolocalization of serum proteins, including albumin, immunoglobulin G (IgG) and IgM, as well as intravenously injected bovine serum albumin (BSA) was examined. Their immunodistribution was more clearly observed in the interstitium by both IVCT and cryobiopsy than conventional methods. IgM was immunolocalized within blood vessels, whereas albumin and IgG were observed in the tumor interstitium. Moreover, intravenously injected bovine serum albumin exhibited leakage from the blood capillaries into surrounding connective tissues in 24 h, but it gradually diffused to the interstitium of the tumor masses during 3 days. These results suggest that molecular leakage from blood capillaries varies significantly in different areas of developing tumors, and that small serum proteins, but not large ones, were abundantly immunolocalized in the tumor interstitium. Both IVCT and cryobiopsy were found to be useful for immunohistochemical studies of soluble molecules in tumors with blood circulation, and may therefore be helpful for further histopathological analyses.

Various microscopic methods have been used to analyze the morphology and molecular distribution of cells and tissues. Using conventional procedures, however, ischemic or anoxic artifacts are inevitably caused by tissue-resection or perfusion-fixation. The in vivo cryotechnique (IVCT) was developed to overcome these problems, and was found to be useful with light microscopy for analyses of the distribution of water-soluble molecules without anoxic effects at high time resolution. But there are limitations to the application of IVCT, such as exposure of target organs of living small animals and immunoreactivity of lipid-soluble molecules owing to freeze-substitution with acetone. Recently, a new cryotechnique called "cryobiopsy" has been developed, which enables one to obtain tissue specimens of large animals including humans without ischemia or anoxia, and has almost the same technical advantages as IVCT. Both IVCT and cryobiopsy complement other live-imaging techniques, and are useful for not only the morphological observation of cells and tissues under normal conditions, but also the preservation of all components in frozen tissue specimens. Therefore, morphofunctional information in vivo would be obtained by freeze-substituion for light or electron microscopy, and also by other analytical methods, such as freeze-fracture replication, X-ray microanalyses, or Raman microscopy. Considering the merits of both IVCT and cryobiopsy, their application should be expanded into other microscopic fields and also from experimental animal studies to clinical medicine.